The present invention relates generally to air cleaning equipment and is particularly directed to an air cleaner of the type which sprays electrically charged liquid droplets into the xe2x80x9cdirtyxe2x80x9d air stream. The invention is specifically disclosed as an air filter that charges semiconductive liquid droplets and sprays them into a chamber in which an air flow that contains entrained dust particles is introduced. The particles are charged to one polarity, the liquid droplets are charged to an opposite polarity, and thus the particles are attracted to the droplets. The droplets are accumulated on a collecting surface, then recirculated and used again to collect further dust particles.
Indoor air includes many small particles which, when inhaled or otherwise contacted by human beings, have a pernicious effect. Dust alone comprises dead skin, dust mite feces, pet dander, and other microscopic (less than 10 microns in size) particles which elicit a human immune response. This is exemplified by dust mite feces, which comprise a wide array of serine and cysteine protease enzymes that cause respiratory irritation and are responsible for many allergy symptoms.
While filtration systems have been used to reduce the amount of small particles present in selected locations, many of the most commonly irritating materials still exist as particles within a range of about 0.1 micron to about 10 microns in size. Filters having pore openings small enough to be effective at removing particles in this size range are known to become easily occluded and generate high backpressure, thereby requiring high power air blowers. Moreover, the ability to maintain proper air conduction through such filters requires a significant amount of electrical energy, is expensive and cumbersome.
Other types of air purifying devices, such as ionic and electrostatic devices, utilize the charge on particles to attract them to a specified collecting surface which is charged at an opposite polarity. Such devices require the collecting surface to be cleaned constantly and have met with limited success in terms of efficiency.
It will be appreciated that small particles can collect in the home and be re-breathed by the occupants without the benefit of elaborate and high power consumption filtration systems found in the public domain. One vestige of prior art systems is their size and high electrical power demand, which affects the cost of operation and the aesthetics of a sizable filtration apparatus.
With regard to the patent literature, an electrostatic scrubber is disclosed in U.S. Pat. No. 4,095,962 (by Richards) which produces highly charged liquid droplets without a concurrent production of a corona by providing a nozzle configured such that the nozzle""s tip forms a substantially uniform electric field over the surface of the liquid on the tip, and this field is large enough to pull off droplets from the tip but not so large so as to create a corona discharge. Selected gas, solid particulates, and liquid mists from gaseous effluents are removed by an electrostatic collector that attracts the highly charged droplets. The droplets are caused to drift, by means of an electric field, through the gaseous effluent to a collecting electrode, thereby absorbing selected gases and aerosol particles, and carrying them to the collecting electrode. The droplet size of the charged droplets is in the range of 30-800 microns radius. One of the recommended scrubbing liquids is ammonium hydroxide, which is used when the effluent gas is sulphur dioxide.
Another patent by Richards, U.S. Pat. No. 6,156,098, also discloses a charged droplet gas scrubber apparatus, which allows scrubbing of uncharged particulates by use of a monopole-dipole attractive force between the charged liquid droplets and the electric dipoles that are induced in the uncharged particulates. The droplet production and charging produces a set of xe2x80x9cspreading liquid sheet electrodesxe2x80x9d in which the droplets are emitted from the edges of the liquid sheets, and these liquid sheets are interspersed with electrically conductive induction electrodes. This configuration again prevents corona discharge while charging the liquid droplets. Once the droplets are charged, they induce an electric dipole moment in the particulate particles. The droplets are collected by an impingement separator, and the liquid is then collected in a sump and strained through a strainer. In Richards ""098, the liquid preferably is a conductive liquid such as tap water, and the size of the droplets is in the range of 25-250 microns diameter. An optimum size of these droplets is stated as being 140 microns. In situations where water is the liquid, the system can be an open-loop system, and the water need not be recirculated. Other liquids could be used, but they must have a minimum conductivity of 50 microSiemens per centimeter (which is 5 Ohmxe2x88x921-meterxe2x88x921). Richards ""098 does not use the electrical charge on the droplets to xe2x80x9ccleanxe2x80x9d the dirt particles in the air. Instead, the Richards device is merely attempping to create water droplets from a stream of water, not necessarily to retain an electrical charge on those droplets.
The two Richards patents are not directed toward room or office air cleaning systems, but are specifically directed toward scrubbing effluent gases, such as those produced in a power plant. Furthermore, the Richards patents use a conductive liquid, and this liquid is not necessarily recirculated, particularly when water is used since it is substantially inexpensive. Another feature of the two Richards patents is that the water droplets are fairly large in size, and again are directed toward removing fairly large particles from effluent gases, at a substantially high temperature in most cases. Such large droplets are not going to be substantially effective in removing particulate matter that is relatively small in particle size.
Another patent in this field is U.S. Pat. No. 3,958,959, by Cohen, which discloses a method of removing particles and fluids from a gas stream using charged droplets having a size between 60-250 microns, in which the preferred size is between 80-120 microns. The droplets are generated by ejecting a stable jet of liquid, such as water, in which the liquid jet is broken into charged droplets by applying an electric potential between the jet and the collecting walls of the scrubber. As the droplets are sprayed between two grounded wall plates, dirty inlet air flows at an angle to the liquid droplet flow direction and, once charged, the droplets are attracted to the walls. Since the droplets are moving at an angle to the direction of movement of the gas stream, this increases the relative velocity between the droplets and the particles. After the droplets impact against the grounded wall plates, they flow to the bottom of the walls and are collected in troughs below the walls, and this liquid thus contains some of the particulates from the gas stream. The resulting slurry is recirculated and the particulate matter is removed by a media filter. In this invention, the xe2x80x9cdroplet drift timexe2x80x9d is generally less than 25 milliseconds.
The droplets in Cohen may consist of water, and in some cases there may be chemical agents added to the water that will react with the gas components that are to be removed. An example of such a chemical agent is sodium hydroxide for removing sulphur dioxide. Examples of collecting efficiency are illustrated in FIG. 12, which shows curves representing the specific collecting area in square feet per cfm (cubic feet per minute) of air volume movement. The curves are generated for mean particle sizes in the range of 1-10 microns, and it is clear that the smaller the particle size, the less the overall collecting efficiency. None of the curves run down to the 0.3 micron particle size, and it is clear that a fairly large specific collecting area would be required to keep efficiencies above 80-90% (and this is only an extrapolation of these curves: nothing is said in the patent document as to whether those curves can realistically be extrapolated in the lower particle size range).
Another patent document in this field is EP 1 095 705 A2, owned by ACE Lab, Inc., which discloses an air cleaning device that produces electrically charged xe2x80x9chyperfine liquid dropletsxe2x80x9d that are formed through an electro-hydrodynamic atomization process which applies a high voltage to capillaries that have nozzles at their tips from which the liquid is ejected in the form of the hyperfine liquid droplets. These liquid droplets xe2x80x9cabsorbxe2x80x9d dust laden air that are flowing through a duct. In actuality, the charged liquid droplets attach themselves to the particles in the dust laden air, and these particles now receive a charge from those liquid droplets. The air flow is directed into an electrostatic dust collector (i.e., an electrostatic precipitator) which has parallel plates that are alternately charged and grounded, thereby forming an electric field that has a polarity opposite to the charge imparted by the liquid droplets. Water is used as an exemplary liquid, because it not only can carry an electrical charge a short distance, but can also humidify the discharged air. Although this EPO document states that the liquid droplets absorb the dust, in reality the opposite is true: the hyperfine liquid droplets are much smaller than the dust, and the main inventive thrust of this invention is a clever way to impart an electrical charge to the dust particles of the inlet air without causing a corona effect. The ACE Lab""s patent (the EP patent) discloses a system where the water droplets are quickly attracted to the particles of dust in the incoming air, and the electrical charge is thereby transferred to the dust. Consequently, a very short relaxation time can be useful and thus water can be used as the liquid medium. This document states that xe2x80x9cfine dustxe2x80x9d that is smaller than 0.1 microns is xe2x80x9cremoved easily and effectively,xe2x80x9d and also states that experimental data showed that the device could remove up to about 90% dust from the air.
One consideration of whole house air cleaners is that, if water is used for the liquid that produces the electrostatically-charged droplets, it must be remembered that microbes can grow in the water. Therefore, it may not be desirable to use water in a recirculating system. However, water is cheap, so an air cleaner could be constructed using water to create the charged droplets if desired, in which case the water could be non-recirculating in a single-pass system. It also must be remembered, however, that water does not easily retain an electrical charge for any appreciable time period, and therefore, has a very short xe2x80x9crelaxation timexe2x80x9d since it is fairly highly conductive. A lesser conductive liquid would have a longer relaxation time and so could retain the electrical charge for a much longer time period. Such a xe2x80x9csemiconductivexe2x80x9d liquid will preferably have the ability to travel several inches or more while retaining the full electrostatic charge that is imparted upon its droplets as they are ejected from the nozzles, thereby having the ability to attract particles from the inlet xe2x80x9cdirtyxe2x80x9d air throughout their entire travel from the nozzle to a collecting plate or container. This principle is utilized in the present invention, as discussed below in greater detail.
Many whole house air cleaners are constructed as electrostatic precipitators, mainly because such air cleaning devices have a fairly low backpressure (i.e., pressure drop) characteristic, thereby enabling a furnace to blow its entire outlet air through an air cleaner without incurring an exceedingly high pressure drop (which would otherwise require a much larger motor and greater electrical power consumption). While electrostatic precipitators are quite common, their dust collecting efficiency specifications leave much to be desired.
For conventional electrostatic air cleaners that are available today, the dust collecting efficiency is typically less than 70% for particles of 0.3 microns, and for the ASHRAE xe2x80x9cdust spot test,xe2x80x9d the dust collecting efficiency is typically less than 78%. Moreover, electrostatic filters need to be kept clean, which is a critical characteristic having negative consequences that is often overlooked by the consumer or user of such electrostatic filters. In standard electrostatic filters, their metal plates or fiber media are easily covered by dust in rather short order, and when that occurs, the electrostatic filters become much less efficient. Furthermore, in fiber electrostatic filters that have a fairly high density of such fibers, once these fibers become covered by dust, the filter can literally become in effect a media filter (i.e., a filter that relies on mechanical means alone to prevent particles of a given size to penetrate therethrough, thus creating a greater backpressure characteristic.)
One example electrostatic air cleaner is manufactured by Honeywell, which has published a data sheet in 2000 for a model number xe2x80x9cF300Exe2x80x9d electronic air cleaner. In this data sheet, Honeywell stated that the xe2x80x9cfractional efficiencyxe2x80x9d of the F300E was 70% on 0.3 micron particles at 500 feet per minute (fpm) air velocity.
This Honeywell document also has a chart called FIG. 1, which shows air cleaner efficiency and pressure drop at various airflow rates. This FIG. 1 shows efficiency ratings based upon the National Bureau of Standards xe2x80x9cinitial dust spot methodxe2x80x9d using the ASHRAE (American Society of Heating, Refrigerating and Air Conditioning Engineers) standard 52.1-92. When analyzing the airflow rates for the largest filter on this chart, which is 20xc3x9725 inches, at a velocity of 500 fpm, the airflow rate would be 1736 cfm (cubic feet per minute). At this airflow rate, the air cleaning efficiency is about 84% at a pressure drop of about 0.11 inches of water column. This would provide a Pressure Adjusted Efficiency (PAE)xe2x80x94which is a new characteristic for air filters created by the present inventors, in which the PAE is equal to the cleaning efficiency divided by the pressure drop-value of 764 (i.e., 84 divided by 0.11).
It is important to note that the above dust spot methodology is referred to as the xe2x80x9cinitialxe2x80x9d dust spot method. This is very important especially with respect to electrostatic air cleaners, since their efficiency drops very quickly once the air cleaning elements begin to accumulate particles. This will be discussed below in more detail.
Another catalog of prior art electrostatic air cleaners has been published by Carrier Corporation in 1999 for an electronic air cleaner sold under the Model Number Series xe2x80x9cAIRAxe2x80x9d in sizes 012, 014, and 020. The largest filter element in this catalog is a 24xc2xdxc3x9720xc2xc filter, Model AIRAAXCC0020. Using the ASHRAE dust spot test, the xe2x80x9cperformance chartxe2x80x9d for this filter at 500 feet per minute air velocity indicates an air cleaning efficiency of about 79% at a backpressure of about 0.07 inches of water column. This would provide a PAE value of about 1128. This very low backpressure specification obviously does not include any pressure drop for ducting, or geometric configuration of the inlet and outlet spaces that bring air to and from the filter element itself.
As can be seen from the above information, particularly the information on the Honeywell F300E air cleaner specifications, it is much easier to obtain a higher cleaning efficiency using the ASHRAE dust spot method than it is for a flow of air containing a single particle size, such as 0.3 micron particles. There are two main reasons for this: in the first place, the ASHRAE dust spot test includes particles of many sizes, a large number of which are greater than 0.3 microns in size; the second reason is that the ASHRAE dust spot test uses particles that often tend to clump together, so that the effective particle size is even larger than the individual particle sizes.
A type of media air filter commonly used in rooms of offices and homes is the HEPA filter, which is specified as having a 99.97% cleaning efficiency for removing particles of 0.3 microns in diameter or larger. This is a standard industry specification, as noted in an EPA publication known as a xe2x80x9cEPA-CICA Fact Sheetxe2x80x9d for fabric filters of the HEPA and ULPA type. HEPA filters typically have a relatively large surface area per unit volume of air to be cleaned moving therethrough, otherwise the pressure drop (or backpressure) would be very high, and thus require a very large motor for operation. The typical pressure drop for a xe2x80x9ccleanxe2x80x9d filter is about 1 inch of water column. As the filter is used and begins to accumulate dust or dirt particles, the pressure drop will increase, and when it reaches between 2 and 4 inches of water column, that typically indicates the end of the service life of the filter. Some HEPA filters when they are xe2x80x9ccleanxe2x80x9d have lower pressure drops in the range of 0.25-0.5 inches of water column.
HEPA filters are typically operated under a pressure of up to four (4) inches of water column, and higher operating pressures may rupture the filter. HEPA filters are used quite often in cleaning the air of individual rooms, but are not common for a xe2x80x9cwhole homexe2x80x9d air cleaning system. The main reason for this fact is that the air flow through a typical furnace or air conditioner of a typical home is much too large for a HEPA filter of a reasonable size. In other words, the HEPA filter would have to be huge to handle the total amount of volume of air that passes through a typical furnace or air conditioner of a home.
One example of the operating characteristics for a HEPA filter is provided at an Internet website for a company named Airclean in the United Kingdom, having an Internet website domain name of xe2x80x9cairclean.co.uk.xe2x80x9d According to one of the tables provided at this website, a HEPA filter having a media size 24 inchesxc3x9724 inches would have a pressure drop of about 0.803 inches of water (200 Pa) at an air velocity of 60 fpm (feet per minute). For this HEPA filter, the PAE characteristic would be a value of about 124.5 (99.97%÷0.803 inches of water).
HEPA-type filters are also used in nuclear environments, although such environments typically require a much greater air cleaning efficiency specification. Consequently, the air flow running through such filter media is generally much slower, and a typical specification is an air velocity of 5 fpm (feet per minute). One paper that describes such filters in some detail is provided in excerpts from the xe2x80x9c16th DOE Nuclear Air Cleaning Conference, Session 10.xe2x80x9d On page 673 of this report, various nuclear HEPA filters running at 5 fpm media velocity exhibit initial pressure drops of between 0.92 and 1.27 inches of water column. Such filters are deemed to come to the end of their useful life when the xe2x80x9cfinalxe2x80x9d pressure drop rises to 3 inches of water column. Such nuclear installations have media filters that can literally fill a large room, since they have to handle a very large volume of air (e.g., for an entire nuclear plant office facility). Consequently, such filters are not considered useful for a home or standard office building.
The table on page 680 of the Nuclear Air Cleaning Conference excerpts is quite revealing with respect to the lifetime of the HEPA filter, as well as its change in pressure drop characteristics over time. For example, one of the filters changed in two months from a pressure drop of 1.04 to 1.37 inches of water column, which is a change of about 32% in two months. Two other filters are shown to have changed their pressure drop characteristics over a four month operating time from 1.1 to 1.5 inches of water column, which is a change of about 36% in backpressure characteristics over that four month time span. This is an increase of almost 9% per month in backpressure for this type of filter. A corresponding pressure increase can be expected in other types of HEPA filters and also ULPA filters as well.
HEPA filters require a certain amount of electrical power for fans to blow the air through the media-type filter. Such fans typically require an electric motor that requires about xc2xd watt to 1 watt per cfm (cubic feet per minute) of fan and air volume movement capacity. When used as a room air cleaner, a typical HEPA filter will circulate about 350 cfm of air volume, for a room about 20 feetxc3x9720 feet in area. The electrical power requirement for such a HEPA room air cleaner is typically in the range of 180-200 watts.
Some disadvantages of using HEPA filters as xe2x80x9croomxe2x80x9d filters are as follows: the HEPA filter is typically noisy, requires a large backpressure for operation, and allows microbes to find their way into the filter and remain there. In situations where microbes are lodged in the filter media, when the filters are changed the microbes can be released into the air. Such filters are often used in confined systems where the air is recirculated, such as in jet aircraft. The microbes will be continually recirculated or will be trapped in the filter media; however, they can still be released into the air when the filter is changed or otherwise xe2x80x9ccleaned.xe2x80x9d
Another characteristic that can be discussed is the xe2x80x9cpermeabilityxe2x80x9d of a filter, which represents a percentage of the xe2x80x9cvoidxe2x80x9d divided by the percentage of xe2x80x9cvolumexe2x80x9d of a filter medium. For HEPA filters, the permeability is typically less than 1%. This means that the air molecules are much more likely to xe2x80x9cbumpxe2x80x9d into the filter media than to be able to pass through the filter media without some type of impact, thus creating a significant backpressure. In the present invention, the permeability of the filter is much greater. One consequence of the HEPA filter""s backpressure characteristic is a substantial noise level generated by the fan, which can be as high as 70 dB for a 20xc3x9720 foot room air cleaner.
Accordingly, it is desirable that an apparatus and method of purifying air be developed which is capable of removing particles of a specified size (about 0.1 micron to about 10 microns) in a manner which is adaptable, non-intrusive, and ergonomically compatible. It is also desirable that a fluid, as well as the requisite attributes thereof, be determined for use with the apparatus and method of purifying air which satisfies the electrical and sprayability demands required for use as the spray. It is further desirable to provide a dynamic electrostatic air cleaning apparatus that improves both backpressure and air cleaning characteristics over those of both HEPA filters and electrostatic precipitators.
Accordingly, it is an advantage of the present invention to provide a dynamic electrostatic air cleaning apparatus that exhibits a substantially high air cleaning efficiency while also exhibiting a substantially low backpressure when air flows therethrough at useful rates for cleaning a whole home, or merely a single room.
It is another advantage of the present invention to provide a dynamic electrostatic air cleaning apparatus that exhibits a substantially high air cleaning efficiency while also exhibiting a substantially low backpressure over a substantial time period of continuous operation without either cleaning or replacing a major component of the apparatus.
It is a further advantage of the present invention to provide a dynamic electrostatic air cleaning apparatus that compares favorably to conventional electrostatic precipitators by exhibiting an air cleaning efficiency greater than 70% at a backpressure of less than 0.2 inches of water column at an air velocity of substantially 2.54 meters per second (500 fpm), when the particles in the inlet air are substantially 0.3 microns in size.
It is yet a further advantage of the present invention to provide a dynamic electrostatic air cleaning apparatus that compares favorably to conventional electrostatic precipitators by exhibiting an air cleaning efficiency greater than 85% at a backpressure of less than 0.1 inches of water column at an air velocity of substantially 2.54 meters per second (500 fpm), when the particles in the inlet air are according to the ASHRAE dust spot test.
It is still a further advantage of the present invention to provide a dynamic electrostatic air cleaning apparatus that compares favorably to conventional HEPA filters by exhibiting an air cleaning efficiency of substantially 99.97% at a backpressure of less than 0.8 inches of water column at an air velocity of substantially 0.4572 meters per second (90 fpm), when the particles in the inlet air are substantially 0.3 microns in size.
It is still another advantage of the present invention to provide an electrostatic air cleaning apparatus that quickly cleans air from an enclosed space by use of electrically charged solid beads or other-shaped particles/objects that attract sub-micron particles entrained in the inlet air, including biohazardous materials, without substantial change to the temperature and humidity of the input air; in this apparatus, the solid beads are not recirculated.
In accordance with a first aspect of the present invention, an apparatus for removing particles from air is disclosed as including at least one inlet for receiving a flow of air, a first chamber in flow (i.e., fluidic) communication with the inlet, wherein a charged spray of semiconducting fluid droplets having a first polarity is introduced to the air flow passing therethrough so that the particles are electrostatically attracted to and retained by the spray droplets, and an outlet in flow communication with the first chamber, wherein the air flow exits the apparatus substantially free of the particles. The first chamber of the apparatus further includes a collecting surface for attracting the spray droplets, a power supply, and a spray nozzle connected to the power supply for receiving fluid, producing the spray droplets therefrom, and charging the spray droplets.
In accordance with a second aspect of the present invention, the apparatus may also include a second chamber in flow communication with the inlet at a first end and the first chamber at a second end, wherein particles entrained in the air flow are charged with a second polarity opposite the first polarity prior to the air flow entering the first chamber. The second chamber of the apparatus further includes a power supply, at least one charge transfer element connected to the power supply for creating an electric field in the second chamber, and a ground element associated with the second chamber for defining and directing the electric field, wherein the air flow passes between the charge transfer element and the ground element.
In accordance with a third aspect of the present invention, the apparatus may further include a fluid recirculation system in flow communication with the first chamber for providing the fluid from the collecting surface to the spray nozzle. The fluid recirculation system includes a device in flow communication with the collecting surface, a reservoir in flow communication with the device, and a pump for providing the fluid to the spray nozzle. The fluid recirculation system may also include a filter positioned between the collecting surface and the pump for removing the particles from the fluid, as well as a device for monitoring the quality of the fluid prior to being pumped to the spray nozzle. A replaceable cartridge may be utilized to house the reservoir, where the cartridge includes an inlet in fluid communication with the collecting surface of the first chamber at a first end and the reservoir at a second end and an outlet in fluid communication with the reservoir at a first end and the pump at a second end.
In accordance with a fourth aspect of the present invention, an apparatus for removing particles from air is disclosed as including at least one defined passage having an inlet and an outlet, wherein each inlet receives a flow of air and the air flow exits the passage at each outlet, and a first area positioned between each inlet and each outlet where a charged spray of semiconducting fluid droplets having a first polarity is introduced within the passage so that particles entrained within the air flow are electrostatically attracted to and retained by the spray droplets. The apparatus further includes a collecting surface associated with the first area of the passage for attracting the spray droplets, as well as a spray nozzle associated therewith for receiving fluid, producing the spray droplets in the first area of the passage, and charging the spray droplets. The apparatus may also include a second area positioned between the inlet and the first area, wherein particles entrained in the air flow are charged with a second polarity opposite the first polarity. The second area includes at least one charge transfer element associated therewith for creating an electric field in the second area of the passage, as well as a ground element associated therewith for defining and directing the electric field in the second area of the passage.
In accordance with a fifth aspect of the present invention, a method of removing particles from air is disclosed as including the steps of introducing a flow of air having particles entrained therein into a defined area and providing a charged spray of semiconducting fluid droplets having a first polarity to the defined area, wherein the particles are electrostatically attracted to and retained by the spray droplets, and attracting the spray droplets to a collecting surface. The method further includes the steps of forming the spray droplets from the fluid and charging the spray droplets. The method preferably includes the step of providing a charge to particles in the air flow at a second polarity opposite of the first polarity. The method may further include one or more of the following steps: filtering the air flow for particles having a size greater than a specified size; monitoring quality of the air flow; filtering the particles from the spray droplets; collecting the spray droplets in an aggregate of the fluid; recirculating the fluid aggregate for use in the spray; and, monitoring quality of the recirculated liquid prior to forming the spray.
In accordance with a sixth aspect of the present invention, a cartridge for use with an air purifying apparatus, wherein a charged spray of semiconducting fluid droplets is introduced to an air flow and collected so as to form a fluid aggregate, is disclosed as including a housing having an inlet and an outlet and a reservoir for retaining the fluid aggregate in flow communication with the inlet at a first end and the outlet at a second end. The cartridge may also include a filter located between the inlet and the reservoir, as well as a pump located between the reservoir and the outlet. The cartridge is configured for the inlet to be in flow communication with the collected fluid aggregate and the outlet to be in flow communication with a device for forming the fluid droplets in the air purifying apparatus. The cartridge housing may function as a collecting surface for the air purifying apparatus and include a spray nozzle associated therewith.
In accordance with a seventh aspect of the present invention, a fluid is disclosed for use as a spray in an air purifying apparatus, wherein particles in an air flow entering the air purifying apparatus are electrostatically attracted to droplets of the spray. The fluid has physical properties which enable a sprayability factor according to a designated algorithm within a specified range, where the sprayability factor is a function of certain physical properties of the fluid which relate to spray droplet size able to be formed and coverage and effectiveness of the spray. Such physical properties of the fluid include flow rate, density, resistivity, surface tension, dielectric constant, and viscosity. The sprayability factor also may be a function of an electric field formed in the air purifying apparatus to which the fluid is introduced. The fluid preferably is semiconducting, nonaqueous, inert, non-volatile and non-toxic.
Additional advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. All percentages, ratios and proportions herein are by weight, unless otherwise specified. All temperatures are in degrees Celsius (xc2x0 C.) unless otherwise specified. All documents cited are in relevant part, incorporated herein by reference.
To achieve the foregoing and other advantages, and in accordance with one aspect of the present invention, an air cleaning apparatus is provided, which comprises: a chamber into which a flow of input air is directed, the input air containing a plurality of particles, the input air becoming a flow of output air after being cleaned within the chamber; at least one nozzle through which a liquid is sprayed into the chamber, the liquid being electrically charged, the liquid becoming separated into a plurality of droplets upon exiting the at least one nozzle; and the chamber being configured to cause the flow of input air and the charged liquid droplets to intermix at an intermix space, wherein the plurality of particles are attracted to the charged liquid droplets, thereby removing a portion of the plurality of particles from the input air, which thus becomes the flow of output air; wherein, when the flow of input air passes through the intermix space of the chamber at an air velocity of substantially 2.54 meters per second (500 fpm), the plurality of particles at substantially 0.3 microns in size is cleaned from the input air at a cleaning efficiency of greater than 70%, at a backpressure of less than 0.2 inches of water column, and without substantial change to a temperature and humidity of the input air.
In accordance with another aspect of the present invention, an air cleaning apparatus is provided, which comprises: a chamber into which a flow of input air is directed, the input air containing a plurality of particles, the input air becoming a flow of output air after being cleaned within the chamber; at least one nozzle through which a liquid is sprayed into the chamber, the liquid being electrically charged, the liquid becoming separated into a plurality of droplets upon exiting the at least one nozzle; and the chamber being configured to cause the flow of input air and the charged liquid droplets to intermix at an intermix space, wherein the plurality of particles are attracted to the charged liquid droplets, thereby removing a portion of the plurality of particles from the input air, which thus becomes the flow of output air; wherein, when the flow of input air passes through the intermix space of the chamber at an air velocity of substantially 2.54 meters per second (500 fpm), the plurality of particles according to the ASHRAE dust spot test is cleaned from the input air at a cleaning efficiency of greater than 85%, at a backpressure of less than 0.1 inches of water column, and without substantial change to a temperature and humidity of the input air.
In accordance with yet another aspect of the present invention, an air cleaning apparatus is provided, which comprises: a chamber into which a flow of input air is directed, the input air containing a plurality of particles, the input air becoming a flow of output air after being cleaned within the chamber; at least one nozzle through which a liquid is sprayed into the chamber, the liquid being electrically charged, the liquid becoming separated into a plurality of droplets upon exiting the at least one nozzle; and the chamber being configured to cause the flow of input air and the charged liquid droplets to intermix at an intermix space, wherein the plurality of particles are attracted to the charged liquid droplets, thereby removing a portion of the plurality of particles from the input air, which thus becomes the flow of output air; wherein, when the flow of input air passes through the intermix space of the chamber at an air velocity of substantially 0.4572 meters per second (90 fpm), the plurality of particles at substantially 0.3 microns in size is cleaned from the input air at a cleaning efficiency of substantially 99.97%, at a backpressure of less than 0.8 inches of water column, and without substantial change to a temperature and humidity of the input air.
In accordance with still another aspect of the present invention, a single-pass air cleaning apparatus is provided, which comprises: a chamber into which a flow of input air is directed, the input air containing a plurality of particles, the input air becoming a flow of output air after being cleaned within the chamber; at least one nozzle through which a plurality of small solid objects are sprayed into the chamber, the solid objects being electrically charged; and the chamber being configured to cause the flow of input air and the charged solid objects to intermix at an intermix space, wherein the plurality of particles are attracted to the charged solid objects, thereby removing a portion of the plurality of particles from the input air, which thus becomes the flow of output air; wherein, when the flow of input air passes through the intermix space of the chamber, a very large portion of the particles exhibiting a sub-micron size are cleaned from the input air without substantial change to a temperature and humidity of the input air, and wherein the solid objects are not recirculated.
In accordance with a further aspect of the present invention, an air cleaning apparatus is provided, which comprises: a chamber into which a flow of input air is directed, the input air containing a plurality of particles, the input air becoming a flow of output air after being cleaned within the chamber; at least one nozzle through which a liquid is sprayed into the chamber, the liquid being electrically charged, the liquid becoming separated into a plurality of droplets upon exiting the at least one nozzle; and the chamber being configured to cause the flow of input air and the charged liquid droplets to intermix at an intermix space, wherein the plurality of particles are attracted to the charged liquid droplets, thereby removing a portion of the plurality of particles from the input air, which thus becomes the flow of output air; wherein, when the flow of input air passes through the intermix space of the chamber, the plurality of particles is cleaned from the input air at a pressure adjusted efficiency (PAE), which represents the cleaning efficiency in percent divided by the backpressure, that does not deviate by more than 25% after two months of continuous use of the air cleaning apparatus.
To achieve the foregoing and other advantages, and in accordance with one aspect of the present invention, an air cleaning apparatus is provided, which comprises: a chamber into which a flow of input air is directed, the input air containing a plurality of particles, the input air becoming a flow of output air after being cleaned within the chamber; at least one nozzle through which a liquid is sprayed into the chamber, the liquid being electrically charged, the liquid becoming separated into a plurality of droplets upon exiting the at least one nozzle; and in which the chamber is configured to cause the flow of input air and the charged liquid droplets to intermix at an intermix space, wherein the plurality of particles are attracted to the charged liquid droplets, thereby removing a portion of the plurality of particles from the input air, which thus becomes the flow of output air; wherein, when the flow of input air passes through the intermix space of the chamber at an air velocity of substantially 2.54 meters per second (500 fpm), the plurality of particles at substantially 0.3 microns in size is cleaned from the input air at a cleaning efficiency of greater than 70%, at a backpressure of less than 0.2 inches of water column, and without substantial change to a temperature and humidity of the input air.
In accordance with another aspect of the present invention, an air cleaning apparatus is provided, which comprises: a chamber into which a flow of input air is directed, the input air containing a plurality of particles, the input air becoming a flow of output air after being cleaned within the chamber; at least one nozzle through which a liquid is sprayed into the chamber, the liquid being electrically charged, the liquid becoming separated into a plurality of droplets upon exiting the at least one nozzle; and in which the chamber is configured to cause the flow of input air and the charged liquid droplets to intermix at an intermix space, wherein the plurality of particles are attracted to the charged liquid droplets, thereby removing a portion of the plurality of particles from the input air, which thus becomes the flow of output air; wherein, when the flow of input air passes through the intermix space of the chamber at an air velocity of substantially 2.54 meters per second (500 fpm), the plurality of particles according to the ASHRAE dust spot test is cleaned from the input air at a cleaning efficiency of greater than 85%, at a backpressure of less than 0.1 inches of water column, and without substantial change to a temperature and humidity of the input air.
In accordance with a further aspect of the present invention, an air cleaning apparatus is provided, which comprises: a chamber into which a flow of input air is directed, the input air containing a plurality of particles, the input air becoming a flow of output air after being cleaned within the chamber; at least one nozzle through which a liquid is sprayed into the chamber, the liquid being electrically charged, the liquid becoming separated into a plurality of droplets upon exiting the at least one nozzle; and in which the chamber is configured to cause the flow of input air and the charged liquid droplets to intermix at an intermix space, wherein the plurality of particles are attracted to the charged liquid droplets, thereby removing a portion of the plurality of particles from the input air, which thus becomes the flow of output air; wherein, when the flow of input air passes through the intermix space of the chamber at an air velocity of substantially 0.4572 meters per second (90 fpm), the plurality of particles at substantially 0.3 microns in size is cleaned from the input air at a cleaning efficiency of substantially 99.97%, at a backpressure of less than 0.8 inches of water column, and without substantial change to a temperature and humidity of the input air.
In accordance with still a further aspect of the present invention, a single-pass air cleaning apparatus is provided, which comprises: a chamber into which a flow of input air is directed, the input air containing a plurality of particles, the input air becoming a flow of output air after being cleaned within the chamber; at least one nozzle through which a plurality of small solid objects are sprayed into the chamber, the solid objects being electrically charged; and in which the chamber is configured to cause the flow of input air and the charged solid objects to intermix at an intermix space, wherein the plurality of particles are attracted to the charged solid objects, thereby removing a portion of the plurality of particles from the input air, which thus becomes the flow of output air; wherein, when the flow of input air passes through the intermix space of the chamber, a very large portion of the particles exhibiting a sub-micron size are cleaned from the input air without substantial change to a temperature and humidity of the input air, and wherein the solid objects are not recirculated.
Still other advantages of the present invention will become apparent to those skilled in this art from the following description and drawings wherein there is described and shown a preferred embodiment of this invention in one of the best modes contemplated for carrying out the invention. As will be realized, the invention is capable of other different embodiments, and its several details are capable of modification in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.